Rolling mill control system

ABSTRACT

A rolling mill control system based upon the constant volume principle and wherein strip length or velocity at the entrance or exit side of the mill is compared with calculated strip length or velocity, to derive an error signal for the rolling mill screwdown and/or a tension regulating device to maintain output gage at a desired value.

United States Patent Murtland, Jr. 1 Jim. 25, 11972 [54] ROLLING MILL CONTROL SYSTEM 3,444,713 5/1969 Bamikel ..72/8 3,564,882 2/1971 Harbaugh et al. ....72/8 [72] Inventor: James B. Murtland, Jr., Natrona Heights,

' d t i I [73] Asslgnee' 31:5:222 d g gg In r nc Primary Examiner-Milton S. Mehr Attorney-Brown, Murray, Flick & Peckham [22] Filed: June 15, 1970 [21] Appl. No.: 46,320

[57] ABSTRACT U-S. Cl ..72/9, 72/12, 72/16 A rolling control ystem based upon the constant volume Cl t J32! 37/12 principle and wherein strip length or velocity at the entrance of Search ..72/6l2, or exit ide of the is compared calculaed trip length or velocity, to derive an error signal for the rolling mill [56] References Cited screwdown and/or a tension regulating device to maintain output gage at a desired value. UNITED STATES PATENTS 3,015,974 1/1962 Qrborn et al ...72 9 99 4 Drawmg Flgum I i l l i SCREW 20 i CONTROL TENS/0N MOTOR I2 I I6 CONTROL 39 /0 355 I14 F38 W E ,/Q32

I 4a 54--@l 56 l INTERNAL 2 COUNTER COUNTER *SH/FT A BINARY a, COMPUTE 62d 1 211 m- GATE L E) 7725 I a, OPERATOR 1 COUNTER RESET 60 suarkAcron DELAY! asset/a3 PATENTED JANZS I972 SHEET 1 OF 4 F ""1I I l l scREw r20 1 c0/vrR0L news/01v MOTOR CONTROL 39 [2% J Wm 35 I14 g a l J 32 O n o 24/@/9\ O /6 Q%\@\ I INTER/m1. 1.

COUNTER COUNTER 52- fLz ISHIFT A DELAY 4a 4o 53 "I 4 I 1 6, compare- 6 BINARY I L262 2d o/a/r/zER 6M5 d BY OPERATOR V COUNTER RESET 60 68 1 66 l SUBTRACTOR DELAy I A l /64 BINARY REG/575R STORE 1.,

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JAMES B. MURTLANO, JR

Attorneys PATENTEDJANZSIHYZ 305350743 SHEET 2 F 4 1" l 1 1 SCREW CONTROL TENS/0N ,34

MOTOR CONTROL 39 V I E 32 28 0 I 26 24 Q E? M IST INTER- A T0 0 A To 0 VAL coy v CONVERTER CONVERTER DELAY '53 44 40 f COMPUTE a 2d w 7 22? GATE z V2624 BY "1 OPERATOR 42 7a 62 v, REGISTER 68 v r r I V .SUBTRACTOR V/REG/S'TER INVENTOR.

JAMES B. MURTLA/VD, JR.

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A l I orneys PATENTEDJANZSISFZ 3 535,7

SHEEI 3 BF 4 I T 1 SCREW MOTOR s: /& CONTROL 39 7 a ,m

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48 5 a INTERNAL COUNTER mun/rm DELAY "1 7 76 BINARY COMM/TE 24 GATE BY DIG/TIZER L2 62d OPERATOR 56" 2 COUNTER 60 r 1 sue TRACTOR DELAY A A 4 r 64 BINARY REGISTER uvvewron.

JAMES B. MURTLA/VD, JR.

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SHEET [If 4 F ""1 l 1 SCREW CONTROL TENS/0N I MOTOR -34 CONTROL /2\ r ,10 sa 9 -74 63 /a2 1 72 INTERVAL A To 0 A TO 0 COUNTER CONVERTER CONVERTER DELAY 5 86' 62 0 i f4 1 j CALCULATE 62d BINARY 6 V 016/ 7725/? 6A V2 OPE/gym? 78' 2 REGISTER 5a r r v SUBTRACTOR -90 2 REGISTER as INVENTOR.

JAMES B. MURTLA/VD, JR.

Attorneys ROLLING MILL CONTROL SYSTEM BACKGROUND OF THE INVENTION As is known, many prior art control systems for rolling mills and the like are such that a mill screwdown is controlled from a gage measurement taken several feet beyond the exit side of the mill. in a system of this type, the material, after reduction, progresses to the gage which may be several feet beyond the bite of the mill rolls before any error present in the material thickness can be detected. This distance from the bite of the rolls to the gage is commonly referred to as transport distance." The time required for the material to reach. the exit gage is denoted as transport time; while the time required to measure the strip exit gage is referred to as sensing time. Transport time and sensing time are major elements in developing error commands. Transport distances of 5 feet or more are common in many prior art rolling mill control systems, meaning that such systems are not capable of detecting an error until 5 feet of material has passed from the bite of the mill rolls. The corrective signal is then transmitted to the mill screwdown; but the measuring gage does not detect the result of this action until 5 feet more of the material has passed through the mill. With a high gain system of this type, a natural frequency of oscillation results; and if this oscillation is left to exist without any attempt to control it, the results are undesirable. That is, for material entering the mill with fairly noticeable changes in gage, the system described would cause wide variations in output gage and in all probability would eventually result in tearing of the ship.

The undesirable transport time and sensing time inherent in conventional feedback gage control systems can be eliminated by a gage control system based on the constant volume princi ple wherein the gage of the strip material is, in :efi'ect, measured directly at the bite of the rolls. Such a system isshown', for example, in U.S. Pat. No. 3,015,974 and copending application Ser. No. 723,121, filed Apr.- 22, 1968, now U.S. Pat. No. 3,564,882, both being assigned to the Assignee of the present application. Control systems of this type are based on the concept that the volume, V,, of material coming out of the mill must be equal to the volume, V,, entering the mill. Thus:

l 1 l 3 2 2 where:

L, length of material entering the mill;

L length of material leaving the mill;

6, gage of material entering the mill;

6, gage of material leaving the mill;

W, width of material entering the mill; andv W, width of material leaving the mill.

ln actual practice, it has been found that the ratio of the width of the material at the input to the millto the'output remains essentially constant. Accordingly, the factors W, and

W, can be eliminated from the foregoing equation resulting in:

in rolling mill control systems of this type based upon the constant volume principle, the input gage, 6,, is measured at a' point ahead of the roll bite each time the strip passes through an interval, such as one inch or less. These gage measurements, then, are advanced through a memory unit'such'as a shift register and are used to derive an error signal for the rolling mill screwdown when the gage fed into the computing circuitry is that of the strip which is then at the bite of the rolls. In this manner, the undesirable transport time and sensing time mentioned above are eliminated.

lr any rolling mill control system, the output gage, 6,, is the ultimate parameter to be controlled. Accordingly, an electrical signal proportional to 6 (desired output gage) isfed into the circuitry for computing an error signal. In U.S. Pat. No.

3,015,974, two control systems are disclosed; In the firstof these, an electrical quantity proportional to L,6, isgenerated and subtracted from a second electrical quantity proportional to L3G to derive an error signal. In another control system shown in the aforesaid U.S. Pat. No. 3,015,974, an error signal for-the rolling mill screwdown is derived by subtracting calculated desired input gage from actual input gage.

Thus:

Error G 6.

Error E, G

G L Error: i za Hence; in theaforesaid copending application, the error signal for the screwdowns derived from a consideration of exit gage parameters rather than input gage parameters.

All of the systems above, while workable, are based upon a comparison of input or output desired gage measurements with a calculated gage measurement, or upon subtraction of the product of input gage times input length from the product of output length times desired output gage.

SUMMARY OF THE INVENTION In accordance with the present invention, it has now been found that instead of comparing actual or desired gages with calculated gages, a rolling mill control system based upon the constant volume principle can be devised wherein actual input length or velocity is compared with calculated input length or velocity. Alternatively, an error signal for the rolling mill control system can'be derived by comparing actual exit length or velocity with'calculated exit length or velocity. Velocity measurements can be used equally as well as length measurements sincethe time factor cancels out from both sides of the constant volume formula. Thus, the present invention provides a means whereby an error signal is derived from either:

V,.and V, are the entering and exit velocities of the strip material; respectively.

' In all of the foregoing cases, either the entrance gage or velocity or the exit gage or velocity is actually measured and compared with a calculated value for the same parameter based upon a consideration of the three remaining parameters in the equation: LIGFZQGM or the equation:

The error signal may be applied to either a rolling mill screwdown, a tension controlling device for the strip material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram of one embodiment of the invention wherein actual input length is compared with calculated input length to derive an error signal;

FIG. 2 is a schematic illustration of another embodiment of the invention wherein actual input velocity of the strip material is compared with calculated input strip velocity to derive an error signal;

FIG. 3 is a schematic diagram of a further embodiment of the invention wherein actual output length of material leaving the rolling mill is compared with calculated output length of material leaving the rolling mill; and

' FIG. 4 is a schematic illustration of still another embodiment of the invention wherein actual output velocity of strip material leaving the rolling mill is compared with calculated exit velocity to derive an errorsignal.

With reference now to the drawings, and particularly to FIG. 1, a single stand rolling mill is shown including an outer housing 12 which supports upper and lower rolls l4 and 16, the spacing or gap between the rolls being controlled by means of a screwdown mechanism generallyindicated by the reference numeral 18. The screwdown mechanism 18, in turn, is controlled by means of a screwdown control which conventionally includes a drive motor mechanically connected to the screwdown mechanism itself, together with electrical controls for the drive motor. Alternatively, the gap between the rolls can be controlled by a wedge or other similar device for varying the spacing between the rolls 14 and 16.

The material being reduced in the mill is identified by the reference numeral 22 and ordinarily comprises strip material which is unwound fromcoil 24 and rewound on coil 26. The

strip material on coil 24 passes over idler roll 28, thence through the roll bite defined between rolls 14 and 16, and then over idler roll to the coil 26. The takeup reel for coil 26 is driven by means of motor 32 controlled by motor control circuit 34 for the purpose of keeping the strip under tension as it is being rolled. As will be appreciated by those skilled in the art, the gage of the strip material can be varied by either varying the spacing between the rolls l4 and 16, by varying the tension on the strip provided by means of motor 32, or by both.

The mill shown in FIG. 1 is of the reversing single stand .type, meaning that during one pass the strip moves from right to left while during the succeeding pass the mill is reversed and the strip moves from left to right. As the mill is reversed, the function of the reels for the two coils 24 and 26 is reversed with the reel for coil 24 acting as the tension reel and the reel for coil 26 acting as a payoff reel. As will be understood, the reel for coil 24 is also provided with a drive motor, not shown. In the following description, it will be assumed that the strip is moving from left to right and that the coil 26 maintains tension on the strip.

At the input to the mill and usually spaced about 5 or 6 feet from the bite of the rolls 14 and 16, is a thickness gage 36 which measures the actual input gage of the strip material entering the mill. 0n the other side of the mill is a second thickness gage 38 which is used to measure the input gage of the strip material when the mill is reversed. However, when the material is passing from left to right as shown in FIG. 1, the gage 38 may be used to monitor the desired gage as selected by an operator as will hereinafter be explained in detail.

The two gages 36 and 38 are typically of the X-ray type;

however in certain cases contact gages may be employed. In

either case, the output of the gage is an analog signal on lead 41, for example, proportional to the gage, 6,, of the entering strip material. This analog signal is applied to a binary digitizer or analog-to-digital converter 40 wherein the gage signal is converted to a plurality of ON or OFF signals representing bits in a binary number. These signals are then applied through gate 42 to the input of a shifi register 44 which advances gage measurements taken, for example, at l-inch intervals along the strip 22 to computation circuitry, generally indicated by the reference numeral 46 in FIG. 1. v

The idler roll 28 is connected to a tachometer pulse generator 48 which will produce an output pulse each time the strip travels through a predetermined distance. Nonnally, the generator 48 will produce a pulse each time the strip passes through a small fraction of an inch such that during l foot of travel of the strip 22, a large number of pulses is generated by the generator 48. These pulses are applied to an interval counter 50 which will produce an output pulse on lead 52 each time the strip passes through a predetermined distance, say 1 foot. The output pulses from the interval counter 50, in turn, are used as shift pulses for the shift register 44 and are also applied through a delay circuit 53 to the gate 42. In this manner, each time the strip 22 moves through 1 foot, a pulse on lead 52 will initially be applied to the shift register 44 to advance the gage measurements stored therein to the next succeeding storage cores in the shift register while advancing the oldest gage measurement stored in the register 44 to the computing circuitry 46. After the information is advanced in this manner, the delay circuit 53 opens the gate 42 to enter a new gage reading into the first core of the shift register. Thus, the cores of the shift register 44 are first shifted to advance information to the computing circuitry 46, followed by the introduction of new information into the unit from gage 36.

It will be appreciated that the shift register 44 serves to store and advance successive entry gage measurements from gage 36 in synchronous correlation with the movement of the strip 22. That is, each time the gate 42 enabled by the interval counter 50, it feeds the instantaneous entry gage measurement to the first core of the shift register 44 which progressively advances these instantaneous measurements from one end of the shift register to the other. The time required to advance from one end of the shift register 44 to the other is equal to the time required for the strip 22 to travel from the gage 36 to the bite of the rolls l4 and 16.

Let us assume, for example, that the gage 36 is spaced 6 feet in front of the bite of the rolls 14 and 16. After the strip 22 has moved 1 foot, the gate 42 opens and the instantaneous gage measurement, in binary form, is fed into the first storage core of the shift register 44. After the strip has traveled another foot, this first gage measurement is shifted to the second storage core and the gate 42 will then open to feed the second instantaneous gage measurement into the shift register. This process continues until 6 feet of material has passed from the gage 36 to the bite of the rolls, at which time the gage measurement at the output of shift register 44 is that taken from a point on the strip which is directly at the bite of the rolls 14 and 16. Thus, length of velocity calculations are made in accordance with the constant volume principle given above, not after the fact, but directly at the bite of the rolls.

Connected to the idler roll 30 is a second pulse generator 54 which, like generator 48, will produce a pulse each time the strip 22 travels through a predetermined distance. For a given length of material, both generators will produce the same number of pulses. The pulses from generator 54, in turn, are applied to an L, counter 56 which has stored therein a number of pulses proportional to the length of the strip material 22 passing out of the mill. The pulses generated by generator 48 will-be less in number than those generated by generator 54 since the strip material, in passing between the rolls l4 and 16, 5

delayed in delay circuit 60. The counters 58 and 56, while being shown herein as reset each time a new gage measurement is taken, need not necessarily be reset over the same time interval. If they are not reset over the same time interval, a second interval counter will be required.

The output of the L counter, in digital form, is applied to the computing circuitry 46 along with the binary signal, 6,, from shift register 44 representing the gage of the material directly at the bite of the rolls 14 and 16. Also applied to the computing circuitry 46 is a signal, G from circuit 62 which is proportional to the desired exit gage of the strip material 22 as determined by the mill operator. The computing circuitry 46 may, for example, comprise part of a general purpose computer or may comprise a separate hardware component for computing the equation:

Since V,G, must always be equal to V 6 as described above, the input length can be computed in circuitry' 46 in accordance with theequation:

where Z, calculated input length;

L, actual output length;

G, actual input gage; and

G desired output gage as determined by the operator.

The electrical signal proportional to 17,, therefore, may be applied to a binary register 64 and compared or subtracted in subtractor 66 from the stored value of L, in counter 58 to derive an error signal on lead 68. This error signal, in turn, is applied back to the screwdown control or, alternatively, to the tension motor control circuit 34 to vary the gage of the strip material 22.

After the mill has been running for a period of time, the actual output gage as measured by gage 38 can be compared with the gage, G selected by the operator in comparison circuit 70 to derive a correction signal for the computing circuitry 46. That is, if the actual output gage is not equal to the desired gage selected by the operator, it is known that the product at the output of the computation circuitry 46 is incorrect or that possibly the L, counter is not registering correctly. This can be corrected by the error signal from comparator 70.

With reference to FIG. 2, a control system is shown which is similar to that of FIG. 1 except that input and output velocity measurements are taken rather than length measurements. Accordingly, elements corresponding to those shown in FIG. 1 are identified by like reference numerals. Again, entry gage measurements, after being converted into binary form in digitizer 40, are passed through gate 42 and entered into shift register 44 where they are advanced in synchronous correlation with the movement of the strip 22 from the gage 36 to the bite of the rolls I4 and 16. In this case, however, a tachometer 72 is connected to idler roll 28 along with pulse generator 48. The tachometer generator 72 will produce an analog signal on lead 74 proportional to the velocity of the entering strip material. This is converted to binary form in analog-to-digital converter 76 and applied to a V, register 78. Similarly, the idler 30 is connected to a tachometer generator 80 which produces an analog signal on lead 82 proportional to the exit velocity of the strip material. This is converted to digital form in analog-to-digital converter 84 and applied to computing circuitry 86 where the equation:

VG 1 2112a is calculated from a consideration of the quantity G, from the shift register 44, V, from the analog digital converter 84 and G from circuit 62 as detennined by the operator. The quantity 7,, comprising calculated input strip velocity, is applied to a second register 88 and subtracted in subtractor to provide an error signal on lead 68 which is fed back to the screwdown control 20 or tension motor control circuit 34.

As was explained above, velocity measurements can be used equally as well as length measurements since velocity appears on either side of the constant volume formula and, consequently, the time element cancels out.

In FIG. 3, another embodiment of the invention is shown which again is similar to that of FIG. 1 except that in this case actual output length, L3, is compared with computed exit length, I}. Thus, the L counter 56 is now connected to subtractor 66 while the output of L, counter is connected to the computing circuitry 46' which computes:

- All a E of course, is computed from a consideration of the entry gage measurement, 6,, from shift register 44, the desired output gage, G from circuit 62 and the input length measurement, L,, from counter 58. The output of the computation circuitry 46, in turn, is applied to binary register 64 and compared with the count of L, counter 56 to derive an error signal on lead 68 which is fed back to the screwdown control 20 or tension motor control circuit 34. Again, since the calculated value of exit length must be equal to lga comparison of the quantity IT, with the actual value of L derives an error signal for gage corrections.

In FIG. 4, still another embodiment of the invention is shown which is similar to that of FIG. 2 and wherein elements corresponding to those of FIG. 4 are identified by like reference numerals. In this case, however, the output of the analog-to-digital converter 76 is connected to the computation circuitry 86'; whereas the output of the analog-to-digital converter 84, comprising a signal proportional to the exit velocity, V is applied to register 78'. Computation circuit 86', in this case, computes:

where the various quantities are the same as those identified above. The output of the computation circuitry 86', comprising a signal proportional to V is applied to register 88' and compared with the actual value of V in register 78' to produce an error signal on lead 68.

Although the invention has been shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

I claim as my invention:

1. In a system for controlling a rolling mill based on the principle of constant volume of material entering and leaving the mill, the combination of means for producing a first electrical signal proportional in magnitude to the desired output gage of strip material leaving the rolling mill, means for producing a second electrical signal which varies as a function of the actual gage of strip material entering the rolling mill, means for producing a third electrical signal which varies as a function of the length of strip material entering the mill over a predetermined period of time, means for producing a fourth electrical signal which varies as a function of the length of strip material leaving the mill over said predetermined period of time, means responsive to said first, second and one of said third and fourth signals for deriving a fifth electrical signal proportional to a calculated value of a quantity which varies as the length of material on one side of the mill varies over said predetermined time interval, and means for comparing said fifth electrical signal with one of said third and fourth electrical signals to derive an error signal for controlling said rolling mill.

2. The system of claim 1 wherein said third and fourth electrical signals vary as a function of the length of strip material entering and leaving said rolling mill over said predetermined period of time.

3. The system of claim 1 wherein said third and fourth electrical signals vary as a function of the speeds of the strip material entering and leaving said rolling mill.

4. The system of claim 1 wherein said first signal is proportional to G the desired output gage of said material leaving the rolling mill; said second signal is proportional to 0,, the actual gage of the material entering the rolling mill; said third and fourth signals are proportional to L, and L,, the actual lengths of material entering and leaving the rolling mill, respectively, over said predetermined period of time; and said fifth signal is proportional to and is compared with said third signal L, to derive an error signal.

5. The system of claim 1 wherein said first signal is proportional to G the desired output gage of strip material leaving the rolling mill; said second signal is proportional to G the actual gage of material entering the rolling mill; said third and fourth signals are proportional to V and V the actual velocities of the strip material entering and leaving the rolling mill, respectively; and said fifth electrical signal is proportional to BE Es-1.

and is compared with said fourth electrical signal to produce an error signal.

7. The system of claim 1 wherein said first signal is proportional to G the desired output gage of strip material leaving the rolling mill; said second electrical signal is proportional to 6,, the actual gage of material entering the rolling mill; said third and fourth signals are proportional to V and V,, the actual velocities of strip material entering and leaving the rolling mill, respectively; and said fifth electrical signal is proportional to and is compared with said fourth electrical signal to derive an error signal.

8. The system of claim 1 wherein said error signal is applied to a screwdown control mechanism for said rolling mill.

9. The system of claim 1 wherein said error signal is applied to a tension regulating device for said rolling mill. 

1. In a system for controlling a rolling mill based on the principle of constant volume of material entering and leaving the mill, the combination of means for producing a first electrical signal proportional in magnitude to the desired output gage of strip material leaving the rolling mill, means for producing a second electrical signal which varies as a function of the actual gage of strip material entering the rolling mill, means for producing a third electrical signal which varies as a function of the length of strip material entering the mill over a predetermined period of time, means for producing a fourth electrical signal which varies as a function of the length of strip material leaving the mill over said predetermined period of time, means responsive to said first, second and one of said third and fourth signals for deriving a fifth electrical signal pRoportional to a calculated value of a quantity which varies as the length of material on one side of the mill varies over said predetermined time interval, and means for comparing said fifth electrical signal with one of said third and fourth electrical signals to derive an error signal for controlling said rolling mill.
 2. The system of claim 1 wherein said third and fourth electrical signals vary as a function of the length of strip material entering and leaving said rolling mill over said predetermined period of time.
 3. The system of claim 1 wherein said third and fourth electrical signals vary as a function of the speeds of the strip material entering and leaving said rolling mill.
 4. The system of claim 1 wherein said first signal is proportional to G2d, the desired output gage of said material leaving the rolling mill; said second signal is proportional to G1, the actual gage of the material entering the rolling mill; said third and fourth signals are proportional to L1 and L2, the actual lengths of material entering and leaving the rolling mill, respectively, over said predetermined period of time; and said fifth signal is proportional to and is compared with said third signal L1 to derive an error signal.
 5. The system of claim 1 wherein said first signal is proportional to G2d, the desired output gage of strip material leaving the rolling mill; said second signal is proportional to G1, the actual gage of material entering the rolling mill; said third and fourth signals are proportional to V1 and V2, the actual velocities of the strip material entering and leaving the rolling mill, respectively; and said fifth electrical signal is proportional to and is compared with said third electrical signal to derive an error signal.
 6. The system of claim 1 wherein said first electrical signal is proportional to G2d, the desired output gage of material leaving said rolling mill; said second electrical signal is proportional to G1, the actual gage of material entering the rolling mill; said third and fourth signals are proportional to L1 and L2, the actual lengths of material entering and leaving the rolling mill, respectively, over said predetermined period of time; and said fifth electrical signal is proportional to and is compared with said fourth electrical signal to produce an error signal.
 7. The system of claim 1 wherein said first signal is proportional to G2d, the desired output gage of strip material leaving the rolling mill; said second electrical signal is proportional to G1, the actual gage of material entering the rolling mill; said third and fourth signals are proportional to V1 and V2, the actual velocities of strip material entering and leaving the rolling mill, respectively; and said fifth electrical signal is proportional to and is compared with said fourth electrical signal to derive an error signal.
 8. The system of claim 1 wherein said error signal is applied to a screwdown control mechanism for said rolling mill.
 9. The system of claim 1 wherein said error signal is applied to a tension regulating device for said rolling mill. 